1. Field of the Invention
The present invention relates to a structure of a lens barrel incorporating a plurality of frame members having a cam mechanism portion in which a cam groove is engaged with a cam follower.
2. Description of the Related Art
A conventional lens barrel has a cam mechanism portion including a cam groove and a cam follower for advancing/retreating a lens frame in the lens optical axis direction. In this lens barrel, the cam groove and the cam follower are disposed at two different frame members, respectively, and rotation of one of the frame members is transmitted to the other frame member for advance/retreat through the cam groove and the cam follower.
FIGS. 14, 15 show a partial sectional view around the cam groove and the cam follower in respective different constructions of the cam mechanism portion of the above conventional lens barrel. In the cam mechanism portion of the conventional lens barrel shown in FIG. 14, a cam groove 101a is provided at a cam frame 101, a cam follower 103 made of metal engaged with the cam groove 101a is pressed into a fitting hole 102a and held at a moving frame 102 supported by the cam frame 101. On the other hand, in another conventional cam mechanism portion shown in FIG. 15, a cam groove 104a is provided at a cam frame 104, and a cam follower 105a engaged with the cam groove 104a is formed by integral molding at a moving frame 105 supported by the cam frame 104.
When the conventional lens having the cam mechanism portion in the structure shown in FIGS. 14, 15 is dropped on the ground in use, an impact force F0 in the optical axis direction acts on the moving frame 102 or 105. The impact force F0 is received by the cam groove and the cam follower interposed between the moving frame 105 and the cam frame 104, but depending on the magnitude of the impact force F0, the cam groove and the cam follower might be damaged, removed or the like.
For example, when a large impact force F0 acts on the cam mechanism portion shown in FIG. 14, there is a fear that a portion where the metal cam follower 103 is in linear contact with the synthetic resin cam groove 101a is strongly brought into contact and the cam groove 101a is plastically deformed as shown in a sectional view illustrating the deformed state of the cam groove and the cam follower in FIG. 16. Also, if the press-fitting length of the cam follower 103 is short, there is a fear that a shaft hole 102a of the moving frame 102 into which the shaft portion 103a of the cam follower 103 is pressed is deformed and the cam follower 103 is removed as shown in a sectional view of FIG. 17 illustrating a state where the cam follower of the cam mechanism portion is removed. Moreover, if a large impact force F0 acts on the cam mechanism portion shown in FIG. 15, there is also a fear that a sheering force and a bending moment act on the cam follower 105a integrally molded at the moving frame 105 and a crack is caused in a root portion 105b as shown in a sectional view in a damaged state of the cam follower in FIG. 18.